1. Technical Field
The present invention relates to an image display apparatus and an image display control apparatus used in the image display apparatus.
2. Related Art
There are known a rear projection type projector configured to project an image on a rear side of a screen using a wide-angle lens or a reflecting mirror and a front projection type projector configured by modifying the arrangement of optical systems being used in the rear projection type projector.
In the rear projection type projector used in an image display apparatus such as a projection television (referred to as the projection TV), a projection optical system is generally designed with the assumption that the distance between a projection lens and the screen is fixed, and the projection lens does not have a zoom function of enlarging or reducing the projection image.
The projection TV generally has a structure in which the optical axis of the projection lens is not perpendicular to a display surface in order to make the apparatus housing thinner.
JP-A-6-138386 is an example of the related art.
Since the projection TV has such a structure, moiré patterns may be generated from optical strain or interference between the screen and projection light. However, the projection optical system only has a function of providing a small zoom as a countermeasure to the moiré patterns. Moreover, in the projection TV, it is impractical to provide the projection optical system with a zoom function for changing a screen size.
The same can be said for the image display apparatus such as the projection TV but also for an image display apparatus (see FIG. 16) using a fixed-focus front projection type projector configured by modifying the arrangement of optical systems being used in the rear projection type projector. As shown in FIG. 16, such an image display apparatus can project a large screen image on a display surface 5 by installing a projector PJ at the proximity of the display surface 5.
It is desirable that programs such as sports or movies are watched on a large screen or a high-definition screen when TV programs are watched on the projection TV. However, it is considered that it is not necessary to watch news or entertainment programs on the large screen or the high-definition screen. In addition, news, entertainment programs, or the like are watched for much time and there are many situation that viewers do not watch the programs with interest and just kill time. In such a situation, it is not considered that the large screen and the high-definition screen are necessarily displayed.
Contrary to such a circumstance, a larger screen and high-definition screen have been progressed and also a brighter screen has been advanced in the projection TV and the like. That is, the programs for which the large screen and high-definition screen are not necessary are displayed on the large screen and high-definition screen. Consumption of unnecessary electric power is undesirable in terms of the energy save. It is also undesirable to consume the unnecessary electric power in the image display apparatus using the fixed focus front projection type projector described above, the direct viewing type liquid crystal TV with a large screen, a plasma TV with large screen, or the like as well as the projection TV.
Meanwhile, the technology disclosed in JP-A-6-138386 described above provides the projection lens making the image display apparatus using a projector smaller and provides a small and thin image display apparatus by using the projection lens. However, there are the foregoing drawbacks even in the technology disclosed in JP-A-6-138386.